Thermal power generation which burns fossil fuel and generates electric power has comparatively low facility cost and the restriction for the installation of an electric power plant is not sever, thermal power generation has been widely used all over the world. Incidentally, the amount of emission of CO2 (carbon dioxide) to cause global warming is increasing continuously every year, therefore, there is the actual circumstances that the reduction of CO2 becomes urgent requirement from a viewpoint of global environment protection. Moreover, since an amount of fossil fuel is limited, fossil fuel should be utilized with saving so as not to be depleted before an energy production technique taking a position of thermal power generation is established. For this reason, although other electric power generating techniques to supplement thermal power generation have been sought, there is a problem that nuclear power generation and hydraulic power generation are hard to be utilized, because the installation of their electric power plants is restricted.
On the other hand, as clean energy which does not give a load to the environment, sunlight energy attracts attention. Generally as a method of changing sunlight into energy, a solar battery has been well known. However, with a current technique, there is the actual circumstance that the electric power generating cost of a solar battery is relatively high in comparison with other plants.
In contrast to this, it has been also considered that sunlight is used directly as energy at relatively low cost Patent Document 1 discloses a technique that sunlight is condensed and changed into heat energy and the heat energy is converted into electrical power. More concretely, in the technique, sunlight is reflected by a large number of reflective mirrors (heliostat) arranged a tower and is condensed into a heat exchanging unit by a condensing mirror mounted on the tower so as to heat the heat exchanging unit, and then the heat energy obtained by the heat exchanging unit is sent to an electric power generating unit, whereby electric power is generated.    Patent document 1: Japanese Patent Unexamined Publication No. 11-119105